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Electrode for stimulating bone growth, tissue healing and/or pain control, and method of use

Electrode for stimulating bone growth, tissue healing and/or pain control, and method of use description/claims

This application claims priority from U.S. Provisional Patent Application Ser. No. 60/813,633 filed on Oct. 3, 2005 and PCT Patent Application No. PCT/US2006/038699 filed on Oct. 3, 2006, which are both incorporated herein by reference in their entirety.

The present invention relates generally to stimulating bone growth and tissue healing, and more particularly to a method and apparatus for stimulating bone growth and tissue healing by applying an electrical current to the bone and adjacent soft tissue through a partially insulated screw.

Bone growth is desirable in many instances, such as when vertebrae in a patient's spine are fused to overcome pain and other effects caused by inter-vertebral movement or intra-vertebral movement. Although bone growth occurs naturally, it can be stunted or stopped by various factors such as tobacco, alcohol and steroid usage, poor bone stock, and age. Moreover, stimulating bone growth to speed recovery is desirable in some instances such as when an injured athlete wishes to return to her sport quickly. Thus, there is a need for stimulating bone growth in individuals.

Bone growth can be stimulated by various means. One such means for stimulating bone growth is by passing an electrical current through the bone. When fusing vertebrae in a patient's spine, various means have been used to stimulate bone growth. For example, some stimulators include wire electrodes embedded in bone fragments grafted to a region of the patient's back containing the vertebrae to be fused. Direct electrical current is applied to the electrodes to stimulate bone growth and fuse the fragments and adjoining vertebrae. To permit the current to be applied for extended periods of time while permitting the patient to be mobile, a generator is connected to the wire electrodes and implanted between the skin and muscle near the patient's vertebral column. The generator provides a continuous low amperage direct current (e.g., 20 μA) for an extended period of time (e.g., six months). After the vertebrae are fused, the generator and leads are surgically removed. Although these embedded electrodes are generally effective, the wire electrodes are susceptible to failure, requiring additional surgery to repair them. Moreover, placement of the wire electrodes is less than precise, allowing some of the current to pass through areas of tissue and bone where it is unneeded and where the current could potentially have adverse effects. Further, imprecise placement may require more energy to be provided to the electrodes than otherwise necessary to be optimally effective. Thus, there are several drawbacks and potential problems associated with devices such as these.

Although small amounts of bone movement can stimulate growth, it is generally desirable to limit movement between the bones or bone fragments being fused. There are several known means for limiting bone movement. Among these means for limiting bone movement are plates, rods and screws. The plates and rods are typically held in position by screws which are mounted in the bone or bones being fused. FIG. 1 illustrates screws (generally designated by 10) driven into a vertebra 12 to immobilize the vertebra. As previously mentioned, the screws 10 are used for attaching rods 14 and/or plates (not shown) to vertebrae to hold the vertebrae in position while they fuse. Although these screws work well for their intended purpose, they do not facilitate electrically stimulating the region. Moreover, if electrical stimulation were applied to bones having conventional screws, the screws could potentially conduct current to areas of tissue and bone where the current is unneeded and where the current could potentially have adverse effects. Thus, there are drawbacks and potential problems associated with conventional screws such as these.

Beyond the well defined role of electrical fields within bone formation, electrical fields have also shown significant promise in aiding healing and recovery in nerve and spinal cord injury. Stimulating tissue healing with electrical currents has been demonstrated to be efficacious in animal models and is now being attempted experimentally in human subjects. Further, spinal cord and nerve root injury has been known to cause associated debilitating pain syndromes which are resist treatment. These pain syndromes also have shown improvement with pulsed electrical stimulation. Given these findings it is envisioned that apparatus providing a specified and confined electrical field through bony constructs and adjacent tissue (e.g., neural tissue) will facilitate an enhanced recovery from spinal cord and nerve injury, including improved functional outcome, better wound healing, and a higher level of pain control.

Briefly, the present invention includes a screw for use in stimulating bone growth, tissue healing and/or pain control. The screw comprises an elongate shaft having a length extending between opposite ends, an exterior surface and a screw thread formed on the exterior surface of the shaft and extending along at least a portion of the length. The shaft has an electrically conducting portion and an electrically insulating portion. The screw also includes a head adjacent one end of the shaft for engaging the screw to rotate the screw and thereby drive it into bone and an electrical conductor electrically connectable to the shaft for conveying current through the shaft to the bone through the conducting portion of the shaft.

In another aspect, the invention includes a method of stimulating bone growth, tissue healing and/or pain control. The method comprises inserting a first electrode into the patient, and inserting a second electrode into the patient at a predetermined distance from the first electrode. An electrical current is passed through the patient between only a portion of the first electrode and only a portion of the second electrode.

In yet another aspect, the invention includes apparatus for stimulating bone growth, tissue healing and/or pain control comprising an electrical power source, and a plurality of electrodes electrically connected to the electrical power source. At least one of the electrodes has a tip adapted for screwing into a patient.

Other features of the present invention will be in part apparent and in part pointed out hereinafter.

FIG. 1 is a horizontal cross section of a conventional electrically conductive screw installed in a vertebra;

FIG. 2 is a side elevation of a screw of the present invention;

FIG. 3 is a cross section of the screw taken along line 3-3 of FIG. 2;

FIG. 4 is an front elevation of a portion of a spine with a first apparatus of the present invention installed thereon; and

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